Method and system for straightening large diameter shafts by selective cold rolling

ABSTRACT

A method and system for straightening large diameter shafts by selective cold rolling by pressing a smaller roller against the shaft with alternating loads as the shaft is slowly rotated.

United States Patent 1 91 Ancarrow, Jr. et al.

[ July 16, 1974 METHOD AND SYSTEM FOR STRAIGHTENING LARGE DIAMETERSHAFTS BY SELECTIVE COLD ROLLING Inventors: John E. Ancarrow, Jr.; RoyL.

Harrington, both of Newport News, Va.

Assignee: Newport News Shipbuilding and Dry Dock Company, Newport News,Va. Filed: Oct. 19, 1972 Appl. No.: 298,978

US. Cl 72/7, 72/81, 72/111 Int. Cl B2ld 3/02 Field of Search 72/110, 7,81, 111, 84;

[56] References Cited UNITED STATES PATENTS 2,827,943 3/1958 Judge, .lr72/11 3,208,250 9/1965 Fournier 72/81 3,213,659 10/1965 Armstrong...72/80 3,583,191 6/1971 Colonius 72/110 Primary Examiner-Richard J.Herbst 5 7] ABSTRACT A method and system for straightening largediameter shafts by selective cold rolling by pressing a smaller rolleragainst the shaft with alternating loads as the shaft is slowly rotated.

9 Claims, 2 Drawing Figures METHOD AND SYSTEM FOR STRAIGHTENING LARGEDIAMETER SHAFTS BY SELECTIVE COLD ROLLING BACKGROUNDOF THE INVENTIONLarge diameter shafts, such as, for example, propellor shafts, aresubject to bending which can occur during manufacturing, processing orin subsequent use. Such bending can occur in the rough forging of theshaft and when machining to final dimensions. In lively forgings thefinal cut for a keyway or the like can create bends. Under somecircumstances, such shafts will become bent after period of use or if apropellor, for example, strikes an obstruction. Acceptable limits ofbend or eccentricity have been established and as a norm, a permissibleeccentricity has been established at 7.4 thousandths of an inch for someoperational uses. Above such a figure, mechanical and technicaldifficulties arise.

Heretofore, methods for the straightening of shafts have been devisedincluding a hot spot method and a peening method. The hot-spot methodinvolves quickly heating a local spot (on the outside of a bend) to anelevated temperature. As a result of the local heat, the heated regiontends to expand, but also due to the elevated heat, the yield strengthof the material is reduced. Due to these combined effects, the metalyields such that the shaft bulges slightly in the heated region. Whenthe heat is removed, the metal then hardens and remains in the bulgedposition and the residual tensile stresses introduced into the outsideof the bend of a shaft tend to straighten the shaft. The hotspot methodis characterized by the following intrinsic disadvantages:

l. The heating process is not accurately controllable. There is noprecise method of determining the amount of heat applied to the shaft.

2. The metallurgy of the shaft can be adversely affected.

3. The process is extremely slow; after each heating the entire shaftmust be allowed to cool to a uniform temperature before the results canbe assessed.

With the peening method, a hammer or equivalent technique is used tohammer or peen the shafting surface on the inside of a shaft bend. Theresidual compressive stresses thereby introduced into the shaft tend tostraighten the shaft. The peening method entails the following intrinsicdisadvantages:

l. The magnitude of the peening effort required to straighten shafts oflarge diameter, especially those of high tensile strength, exceeds thatwhich can be accomplished with the usual peening techniques.

2. The residual stresses introduced into the shaft are distributednon-uniformly.

3. Peening subjects the shafting surface to possible damage.

4. Due to the superficial nature of the compressive residual stressesintroduced, efforts to improve the surface finish of the shafting afterpeening by cutting a small amount of metal from the shaft will tend todestroy the effect achieved because the residual stresses in the metalremoved from the shaft will not be uniform around the circumference ofthe shaft.

' The present invention, utilizing selective cold rolling of a portionof the shafting surface for straightening large diameter shafts,provides capabilities not obtainable with these prior known methods.

SUMMARY OF THE INVENTION The selective cold rolling method of theinvention involves the use of cold rolling equipment such as is commonlyused in connection with propellor shafts on ships, however, instead ofusing a constant roller load and introducing residual compressivestresses uniformly around the circumference of a shaft, the roller loadis varied selectively so as to use a higher roller load, with consequenthigher residual compressive stresses, on the inside of a bend therebytending to straighten the shaft. The selective cold rolling of a shaftis accomplished by pressing a small roller against the shaft withalternating loads as the shaft is slowly rotated. A specified length ofthe shaft is rolled by slowly advancing the roller along the shaft as itrotates.

The roller has a crowned face and is sized with radii of curvature whichare much smaller than those of the shaft such that a very smallelliptical contact area exists between the roller and the shaft. Thecombination of a heavy roller load on the shaft and the small contactarea results in very large contact stresses between the shaft androller. These stresses cause a yielding of the shaft material near thesurface which then leaves a residual compressive stress in the materialadjacent to the surface. By controlling the roller load, the magnitudeand depth of the residual stress can also be controlled. The residualstress over the yielded depth actually produces a residual force in thearea adjacent to the shaft surface and it is this residual force whichis utilized to straighten a shaft.

Advantages associated with the selective cold rolling method include thefollowing:

1. The variables required to straighten a shaft can actually becalculated. 2. The method is easily controlled such that predictableresults can be achieved. 3. The residual stresses introduced in theshaft are not distributed erratically. 4. The results achieved can beassessed immediately after a rolling operation. 5. The straightening canbe accomplished by introducing residual compressive stresses completelyvaround the shaft circumference but more deeply on one side of the shaftthan the other; this permits a small amount of metal to be removed fromthe shaft without affecting the straightening results achieved.

6. The metallurgy of the shaft material is not adversely affected.

Other objects and advantages of the invention will be more readilyapparent from the following detailed description of an embodimentthereof when taken together with the accompanying drawings in which:

FIG. 1 is a schematic plan view of a shaft straightening machine inaccordance with the invention; and

FIG. 2 is a graph showing results obtained in practice of the presentinvention.

Referring now in detail to the drawings, there is shown in FIG. 2 theeccentricity in a shaft before and after straightening in accordancewith the invention. The figures are for a 16 inch diameter shaft 470inches long. It is to be noted that the maximum eccentricity was foundat approximately position H and indicated in inches fromthe shaft end.The eccentricity is indicated in thousandths of an inch. The shaft whatwas straightened had an initial eccentricity of approximately 17.5thousandths of an inch and after straightening, the maximum eccentricitywas approximately 3 thousandths of an inch. This eccentricity is wellwithin the allowable limit as indicated above of 7.5 thousandths of aninch.

Apparatus usable in practicing the invention is shown schematically inFIG. 1 and basically is designed to accomplish a plurality of functions.The shaft to be straightened must be freely supported at two points withprovisions to rotate it. The alternating roller loads have to be appliedto the shaft as it turns without deflecting the shaft excessively, theroller loads must be adjustable, and the advance of the roller along theshaft has to be adjustable. A more detailed discussion of the apparatuswill follow hereinafter but prior to this a discussion of the principlesis deemed appropriate.

The use of a constant roller load around the shaft circumference would,of course, have no effect on the shaft since the forces on oppositesides oppose one another. However, the actual straightening processinvolves the application of a heavy roller load over a portion of theshaft circumference with a lesser load over the remainder of the shaftcircumference. The residual force in the shaft produced by the heavyroller load is opposed by a smaller force on the opposite side, thus acouple is produced in the shaft due to the two different residualforces.

Since the residual forces produced in the sahft are due to compressivestresses, they tend to push or stretch the shaft in the longitudinaldirection. With the heavier force pushing on one side, the coupleproduced in the rolled area causes the shaft to bow away from the heavyload, that is, a bend is produced with the convex side centered on thearc of the heavy roller load. Therefore, to straighten an existing bendin a shaft, the heavy roller load is located on the concave side of thebend in order to bend the shaft in the opposite direction until it isstraight.

A single roller load over an arc would produce a straightening couple;however, the use of a reduced load over the remaining shaftcircumference is necessary to facilitate machining the shaft afterstraightening. The reduced load over the entire circumference creates auniform force around the shaft down to a depth corresponding to thereduced load with the effective straightening couple being produced overthe increased depth of yielding in way of the heavy load. Therefore,after straightening the shaft, the surface of the shaft in way of therolled area can be machined down to a depth corresponding to the reducedload without upsetting the non-uniform force and straightening couple.This allows final machining of a shaft after straightening withoutaffecting its straightness.

In order to assure that an area is fully cold rolled, the advance of theroller along the shaft during one shaft revolution cannot exceed theminor semi-axis of the An analytical procedure is used to determine therolling variables based on the dimensions of a shaft, the location ofthe bend in a shaft, and the eccentricity of the shaft. With thisinformation, the location and length to be rolled, the two roller loads,the rolling arcs for the two loads, and the speed of advance can all becalculated.

The shape and eccentricity of a shaft is determined by supporting theshaft at two points and rotating it. Dial indicators are placed atregular intervals along its length, and the indicator readings or shaftrunouts are recorded for every of rotation. The eccentricity values(runout divided by two) are then plotted on a polar plot (lookingaxially along the shaft) to determine the angle at which the maximumeccentricities occur. Having determined this angle the shafteccentricities are then plotted and the longitudinal location of thebend and the shaft eccentricity can then be determined. In some casesthe plots may show several bends in one or more planes which indicatesthe need to roll the shaft in several different locations with theproper rolling variables determined for each location.

As pointed out above, several functions are required as regards theapparatus. The shaft has to be freely supported at two points withprovisions to rotate it. The alternating roller loads have to be appliedto the shaft as it turns without deflecting the shaft excessively, theroller loads must be adjustable, and the advance of the roller along theshaft has to be adjustable. FIG. 1 schematically shows such apparatusused to straighten a shaft by selective cold rolling.

The shaft 10 is supported by lathe centers 12 at each end as shownalthough the shaft could be supported by steady rests on its span,rather than with lathe centers, or by any other method which would allowthe shaft to turn. The shaft is driven by a variable speed drive motor14 in a usual manner. A carriage assembly 16 is operatively mounted onthe machine and driven in a known manner through a carriage drive screw18.

The actual cold rolling assembly consists of two diametrically opposedhydraulic cylinders, including backup cylinder 20 and roller cylinder22. Cold rolling roller 24 is actuated by roller cylinder 22 and ababbitted backup pad 26 is actuated by backup cylinder 20. The cylinders20 and 22 are of the same size and supported on a common carriage andare cross-connected so that the roller load on the shaft is opposed bythe load on the babbit pad, thus the babbit pad simply acts as a backupsupport for the heavy roller load and prevents the roller forces fromdeflecting the shaft and transmitting any loads to the shaft supports.Additionally, the use of the two cross-connected cylinders with thebalanced loads allows the roller and pad to freely follow the movementof a bent shaft as it rotates. Since two different roller (and backuppad) loads are required as the shaft rotates, a hydraulic oil supplycapable of supplying the different pressures is required. To this end ahigh pressure oil supply source 28 is provided and a low pressure source30 is also provided. The high and low pressures are alternately appliedto the cylinders 20 and 22 by means of an electrically or pneumaticallyoperated two position valve 32. The two hydraulic pressures can besupplied by two adjustable pumps, a single pump feeding two adjustableregulators or relief valves, or by gas-oil accumulators with adjustablepressures.

The two position valve 32 is controlled by a switch, such as a camswitch 34 which is located adjacent to shaft and is actuated by a cam 36attached to the shaft. The cam 36 is simply, in the shown embodiment, aflexible strip which is taped to the shaft over the arc of either theheavy load or light load, depending on how the valve is piped to the oilsupplies. In either case, the cam is located to actuate the switch andthe valve such that the valve routes the high pressure oil to the rollerover the desired arc and the low pressure oil over the remainingcircumference of the shaft.

In operation, the carriage assembly which supports the two cylinders isslowly advanced down the shaft as the shaft is rotated. The advance orfeed on the carriage is fully adjustable to allow for different rollerloads. The apparatus as shown utilizes a lathe normally used to machineshafting. The shaft is rotated by the headstock. The carriage assemblyfor the cylinders is designed to rest on a carriage for a tool post.Since the tool post is moved along the lathe by the lead screw and has afully adjustable speed, this also provides an adjustable advance speedfor the roller. To simplify piping, the accumulators and associatedpiping are located on the carriage assembly. Flexible hoses are used toconnect the accummulators to the supply source. The roller as used has acrowned face and is sized with radii of curvature which are much smallerthan those of the shaft, such that a very small elliptical contact areaexists between the roller and the shaft. The combination of a heavyroller load on the shaft and the small contact area results in verylarge contact stresses between the shaft and roller. These stressescause a yielding of the shaft material near the surface which thenleaves a residual compressive stress in the material adjacent to thesurface. By controlling the roller load, the magnitude and depth of theresidual stress can also be controlled. The residual stress over theyielded depth actually produces a residual force in the area adjacent tothe shaft surface and it is this residual force which is utilized tostraighten the shaft.

Following is an operative set of instructions for straightening, by coldrolling, of a propellor shaft, such as indicated at 10 in FIG. 2.

1. Determine Location & Magnitude of Bend Prior to straightening,determine the location and magnitude of the bend by supporting the shaftsection between lathe centers with no steady rests and take dialindicator readings atleast every four feet along the shaft length.Tabulate the runout at each station by clock positions. Additionalreadings may be required to determine the exact location of maximumrunout. Based on the measured eccentricity (one half of runout) and thelocation of the bend, calculate the two roller loads and arcs and therolling length required to straighten the shaft. Mark the arc for theheavy load on the side opposite the maximum runout. Also mark therolling length on the shaft with its location centered about the pointof maximum runout. This is the potential area to be cold rolled.

2. Method of Cold Straightening a. Set up cold rolling machine as shownin FIG. 1.

b. Charge the HP. accumulator to a pressure corresponding to the heavyload.

c. Charge the LP. accumulator to a pressure corresponding to the lightload.

d. Support the shaft in lathe centers with one steady rest locatedforward of the area to be cold rolled.

e. Cold rolling is to be initially accomplished for a distance ofapproximately one half of the calculated length.

f. Rotate the shaft to obtain a shaft surface speed of about 15 feet perminute (approx. 2 RPM) and set the cold rolling machine at the rate offeed corresponding to the light roller load.

g. As the shaft rotates and the beginning of the heavy load arcapproaches the hardening roller open valve 32 to high pressure. As theend of the heavy arc approaches the hardening roller, close valve tohigh pressure and open valve to low pressure. As the beginning of theheavy arc approaches the hardening roller again close valve to lowpressure and open valve to high pressure. Repeat this cycle everyrevolution, transferring fluidas necessary from the LP. to the H.P.accummulator until the cold rolling operation has continuedapproximately one half of the calculated length.

h. lsolate the H.P. and LP. accumulators and back the rollerand steadyrest away from the shaft. Take dial indicator readings to determine theamount of runout with the shaft supported by lathe centers only.

i. The next step will depend upon the determined amount of movement ofthe shaft due to the initial cold rolling. If the shaft has straightenedconsiderably more or less than expected for rolling over half of thecalculated length, some adjustment to the roller loads or lengths may benecessary. If the shaft is straightening as expected then rolling overthe remaining length can be completed.

j. After the shaft has been straightened within the desired tolerancesor to the maximum extent feasible, dial indicator readings are taken atthe locations used in Step 1 and recorded.

We claim:

I l. A method of straightening a bent shaft comprising:

A. supporting and rotating the shaft; B. applying alternately a heavyroller load and a lesser roller load to the surface of the shaft whilerotating, and wherein:

i. the roller load is applied by a roller having a crowned face with aradius of curvature considerably smaller than that of the shaft suchthat a very small elliptical contact area exits between the roller andthe shaft, the roller load being such that residual compressive stressesare induced in the material of the shaft adjacent to the surface;

ii. during a revolution the heavy roller load is applied to the concaveside of the bend, with the lesser load being applied over the remainingshaft circumference, the resulting compressive stresses therebyproducing a residual force which straightens the shaft;

iii. that side of the shaft opposite to the roller loads is supportedwith a back-up pad to prevent roller forces from deflecting the shaft;and

C. advancing the position of application of the roller loads along theshaft as it rotates.

2. A method as claimed in claim 1, wherein an assembly for the methodconsists of two diametrically opposed hydraulic cylinders with theroller actuated by one cylinder and a back-up pad supported by the othercylinder, said cylinders being cross-connected to a fluid pressuresource so that the roller load on the shaft is opposed by the back-uppad.

3. A method as claimed in claim 1, wherein the ad vance of the rolleralong the shaft during one shaft revolution does not exceed the minorsemi-axis of the elliptical contact area between the shaft and roller.

4. A method as claimed in claim 3, including determining the locationand length to be rolled, the two roller loads, the size and shape of theroller, the rolling arcs for the two loads, and the speed of advancebased on measurements of the eccentricity of the shaft.

5. A method as claimed in claim 4, including marking an arc on the sideopposite the maximum runout for a substantial distance axially on eitherside of the point of maximum runout and indicating the potential area tobe cold rolled, high roller pressure being initiated as the beginning ofthe marked arc approaches the hardening roller and, as the end of thearc approaches the hardening roller, high pressure being terminated andlow pressure being applied, with the cycle being repeated for each shaftrevolution.

6. A method as claimed in claim 2, including high and low pressuresources for said cylinders, and a twoposition valve operable forselectively applying high or low pressures to said cylinders.

7. A method as claimed in claim 6, including sensor means adjusted toactuate the valve such that the valve routes the high pressure oil tothe roller over the desired arc of the shaft and the low pressure oilover the remaining circumference of the shaft.

8. A method of straightening a bent shaft comprising:

A. supporting and rotating the shaft;

B. cold rolling the shaft by applying alternately a heavy roller loadand a lesser roller load to the surface of the shaft while rotating toproduce internal stress in the shaft, and wherein:

i. the roller load is applied by a roller having a crowned face with aradius of curvature considerably smaller than that of the shaft suchthat a very small elliptical contact area exists between the roller andthe shaft, the roller load being such that residual compressive stressesare induced in the material of the shaft adjacent to the surface;

ii. during a revolution the heavy roller load is applied to the concaveside of the bend, with the lesser load being applied over the remainingshaft circumference, the resulting compressive stresses therebyproducing a residual force which straightens the shaft;

iii. that side of the shaft opposite to the roller loads is supportedwith a back-up pad to prevent roller forces from deflecting the shaft;and

C. advancing the position of application of the roller loads along theshaft as it rotates. 9. A method of straightening a bent shaftcomprising:

A. supporting and rotating the shaft;

B. cold working the surface of the shaft by applying alternately to thesurface thereof through a roller a heavy roller load and a lesser rollerload while rotating the shaft to produce internal stress therein,

and whereini i. the roller load is applied by a roller having a crownedface with a radius of curvature considerably smaller than that of theshaft such that a very small elliptical contact area exists between theroller and thejshaft, the roller load being such that residualcompressive stresses are induced in the material of theshaft adjacent tothe surface;

ii. during a revolution the heavy roller load is applied to the concaveside of the bend, with the lesser load being applied over the remainingshaft circumference, the resulting compressive stresses therebyproducing a residual force which straightens the shaft;

iii. that side of the shaft opposite to the roller loads is supportedwith a back-up pad to prevent roller forces from deflecting the shaft;and

C. advancing the position of application of the roller loadsprogressively along the shaft as it rotates, whereby the internal stressresults in straightening of the shaft.

1. A method of straightening a bent shaft comprising: A. supporting and rotating the shaft; B. applying alternately a heavy roller load and a lesser roller load to the surface of the shaft while rotating, and wherein: i. the roller load is applied by a roller having a crowned face with a radius of curvature considerably smaller than that of the shaft such that a very small elliptical contact area exits between the roller and the shaft, the roller load being such that residual compressive stresses are induceD in the material of the shaft adjacent to the surface; ii. during a revolution the heavy roller load is applied to the concave side of the bend, with the lesser load being applied over the remaining shaft circumference, the resulting compressive stresses thereby producing a residual force which straightens the shaft; iii. that side of the shaft opposite to the roller loads is supported with a back-up pad to prevent roller forces from deflecting the shaft; and C. advancing the position of application of the roller loads along the shaft as it rotates.
 2. A method as claimed in claim 1, wherein an assembly for the method consists of two diametrically opposed hydraulic cylinders with the roller actuated by one cylinder and a back-up pad supported by the other cylinder, said cylinders being cross-connected to a fluid pressure source so that the roller load on the shaft is opposed by the back-up pad.
 3. A method as claimed in claim 1, wherein the advance of the roller along the shaft during one shaft revolution does not exceed the minor semi-axis of the elliptical contact area between the shaft and roller.
 4. A method as claimed in claim 3, including determining the location and length to be rolled, the two roller loads, the size and shape of the roller, the rolling arcs for the two loads, and the speed of advance based on measurements of the eccentricity of the shaft.
 5. A method as claimed in claim 4, including marking an arc on the side opposite the maximum runout for a substantial distance axially on either side of the point of maximum runout and indicating the potential area to be cold rolled, high roller pressure being initiated as the beginning of the marked arc approaches the hardening roller and, as the end of the arc approaches the hardening roller, high pressure being terminated and low pressure being applied, with the cycle being repeated for each shaft revolution.
 6. A method as claimed in claim 2, including high and low pressure sources for said cylinders, and a two-position valve operable for selectively applying high or low pressures to said cylinders.
 7. A method as claimed in claim 6, including sensor means adjusted to actuate the valve such that the valve routes the high pressure oil to the roller over the desired arc of the shaft and the low pressure oil over the remaining circumference of the shaft.
 8. A method of straightening a bent shaft comprising: A. supporting and rotating the shaft; B. cold rolling the shaft by applying alternately a heavy roller load and a lesser roller load to the surface of the shaft while rotating to produce internal stress in the shaft, and wherein: i. the roller load is applied by a roller having a crowned face with a radius of curvature considerably smaller than that of the shaft such that a very small elliptical contact area exists between the roller and the shaft, the roller load being such that residual compressive stresses are induced in the material of the shaft adjacent to the surface; ii. during a revolution the heavy roller load is applied to the concave side of the bend, with the lesser load being applied over the remaining shaft circumference, the resulting compressive stresses thereby producing a residual force which straightens the shaft; iii. that side of the shaft opposite to the roller loads is supported with a back-up pad to prevent roller forces from deflecting the shaft; and C. advancing the position of application of the roller loads along the shaft as it rotates.
 9. A method of straightening a bent shaft comprising: A. supporting and rotating the shaft; B. cold working the surface of the shaft by applying alternately to the surface thereof through a roller a heavy roller load and a lesser roller load while rotating the shaft to produce internal stress therein, and wherein: i. the roller load is applied by a roller having a crowned face with a radius of curvature considerably smaller than that of the sHaft such that a very small elliptical contact area exists between the roller and the shaft, the roller load being such that residual compressive stresses are induced in the material of the shaft adjacent to the surface; ii. during a revolution the heavy roller load is applied to the concave side of the bend, with the lesser load being applied over the remaining shaft circumference, the resulting compressive stresses thereby producing a residual force which straightens the shaft; iii. that side of the shaft opposite to the roller loads is supported with a back-up pad to prevent roller forces from deflecting the shaft; and C. advancing the position of application of the roller loads progressively along the shaft as it rotates, whereby the internal stress results in straightening of the shaft. 